All live, I guess? If you can only lay one track down first, drums is good.That sets the tempo (with a good drummer!) Drum breaks can always be overdubbed. Then the rest of the rhythm section - guitar (rhythm) and bass - any order.Assuming the drummer can play to a click track, it's worth including one. If not, and the drummer fluctuates, on what may essentially be a dance track, it may need to be quantised later. It may well help if the others - bass, guitar, vox play along to be heard only in the drummer's cans. It makes life easier for the drummer to have that to play along to, rather than just play in isolation.
That all gives the piano, orchestra and vocals something to latch onto.
Bear in mind that any rough bits can be overdubbed at a later stage, and it rather depends what the 'orchestra' is adding to the piece.If the piece is supposed to go out of time, then it's pretty important for the drumer to hear the others.